1. Field of the Invention
The present invention relates to an optical integrated device, a method for detecting light, an optical pickup, and an optical disc apparatus. In particular, the present invention relates to an optical disc apparatus that records information on an optical disc and reproduces information from the optical disc.
2. Description of the Related Art
Optical disc apparatuses widely used today emit light beams from laser diodes of optical pickups, irradiate optical disks with the light beams through objective lenses, and read reflected light of the light beams so as to reproduce information.
Moreover, optical disc apparatuses can record information on optical discs by irradiating the optical discs with light beams and changing the local reflectivity of the optical discs.
In general, an optical disc apparatus focuses a light beam on a desired target position of an optical disc by performing servo control of an objective lens.
In practice, an optical disc apparatus generates a focus error signal and a tracking error signal in accordance with reflected light that has been received. The focus error signal indicates the amount of deviation of a focal point of a light beam from a target position in a focusing direction. The tracking error signal indicates the amount of deviation in a tracking direction. The focusing direction refers to a direction toward or away from the surface of an optical disc. The tracking direction refers to the radial direction of the optical disc.
The optical disc apparatus performs the servo control of the objective lens using the focus error signal and the tracking error signal. Therefore, the qualities of the focus error signal and the tracking error signal determine the accuracy of the servo control in the optical disc apparatus.
In particular, in an optical disc apparatus, when an objective lens moves in the tracking direction due to servo control in the tracking direction (when so-called “lens shift” occurs), a position at which reflected light is received is shifted and thereby the qualities of the error signals are reduced.
To address this problem, Japanese Unexamined Patent Application Publication No. 2007-265595, for example, discloses an optical disc apparatus that detects the amount of lens shift by intentionally blocking or splitting a portion of reflected light and receiving the reflected light with a plurality of light receiving regions, and adjusts error signals using the detection results so as to increase the quality of the error signals (see FIG. 5 of the Publication).